/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.values;



import com.bff.gaia.unified.sdk.Pipeline;

import com.bff.gaia.unified.sdk.transforms.PTransform;

import com.bff.gaia.unified.sdk.io.TextIO;

import com.bff.gaia.unified.sdk.transforms.Create;



import java.util.Collections;

import java.util.Map;



/**

 * {@link PBegin} is the "input" to a root {@link PTransform}, such as {@link TextIO.Read Read} or {@link

 * Create}.

 *

 * <p>Typically elided by simply calling {@link Pipeline#apply(String, PTransform)} or {@link

 * Pipeline#apply(PTransform)}, but one can be explicitly created by calling {@link Pipeline#begin}

 * on a Pipeline.

 */

public class PBegin implements PInput {

  /** Returns a {@link PBegin} in the given {@link Pipeline}. */

  public static PBegin in(Pipeline pipeline) {

    return new PBegin(pipeline);

  }



  /**

   * Like {@link #apply(String, PTransform)} but defaulting to the name of the {@link PTransform}.

   */

  public <OutputT extends POutput> OutputT apply(PTransform<? super PBegin, OutputT> t) {

    return Pipeline.applyTransform(this, t);

  }



  /**

   * Applies the given {@link PTransform} to this {@link PBegin}, using {@code name} to identify

   * this specific application of the transform.

   *

   * <p>This name is used in various places, including the monitoring UI, logging, and to stably

   * identify this application node in the job graph.

   */

  public <OutputT extends POutput> OutputT apply(

      String name, PTransform<? super PBegin, OutputT> t) {

    return Pipeline.applyTransform(name, this, t);

  }



  @Override

  public Pipeline getPipeline() {

    return pipeline;

  }



  @Override

  public Map<TupleTag<?>, PValue> expand() {

    // A PBegin contains no PValues.

    return Collections.emptyMap();

  }



  /////////////////////////////////////////////////////////////////////////////



  /** Constructs a {@link PBegin} in the given {@link Pipeline}. */

  protected PBegin(Pipeline pipeline) {

    this.pipeline = pipeline;

  }



  private final Pipeline pipeline;

}